Production of titanium



- 'iNvENToR Z LAWRENCE'U. REIMERT ATTORNEYS March 19, 1963 .1. REIMERT PRODUCTION OF TITANIUM Filed Mairch 29, 1960 FIG. 1

FIG. 2

United States Patent 3,982,159 PRGDUCTIQIN @F TITANIUM Lawrence J. Reimert, Schneclrsville, Pa, assignor to The New Jersey Zinc Company, New York, N.Y., a corporation of New Jersey Filed Mar. 29, 1960, Ser. No. 18,313 7 Claims. (Cl. 2tl4-64) This invention relates to the production of metallic titanium and, more particularly, to a novel method of effecting electrodeposition of titanium metal from a fused salt bath.

An electrolytic operation which is particularly characterized by the production of relatively coarse electrodeposited metallic titanium is one wherein the titanium is deposited on that surface of a cathode which is distal with respect to an anode in direct bath-communication with the cathode. That is, a fused chloride salt bath containing titanium trichloride and titanium dichloride is electrolyzcd between the anode and cathode while titanium tetrachloride is introduced into that portion of the bath which is in contact with the distal surface of the cathode (and hence called the catholyte), the anode surface and the effective distal cathode surface (i.e. the surface of the titanium deposit) being in direct communication with one another through the bath uninterrupted by any physical barrier other than a pervious deposit of metallic titanium on the distal surface of the cathode which divides the bath into the aforesaid catholyte and a remaining portion called the anolyte. The electrolytic conditions are so maintained between the electrodes, and the anolyte and catholyte compositions are so maintained, that a porous deposit of metallic titanium is formed predominantly on the aforementioned distal surface of the cathode. Such an operation is described in the United States patents to Reimert and Fatzinger, No. 2,848,397; Andrews, No. 2,900,318; and Barnett, No. 2,908,619.

The successful operation of an electrolytic cell according to the foregoing procedure depends upon the rapid initial deposition, and subsequent maintenance, of a pervious layer of titanium metal on the cathode in order to prevent significant diffusion of titanium ions from the catholyte into the anolyte. The United States patent to Barnett, No. 2,908,619 describes the addition of oxygencontaining metallic titanium fines to the catholyte as an expedient for accelerating the formation of this desired layer of titanium on the cathode, and the co-pending application of Reimert and Fatzinger, Serial No. 722,408, filed March 19, 1958, now US. Patent No. 2,975,111, describes the use of an auxiliary cathode in contact with the catholyte in order to build up a concentration of lower valence titanium ions in the catholyte conducive to the deposition and maintenance of the desired layer of titaninum on the cathode.

When a satisfactory concentration of lower valence titanium ions is established in the catholyte portion of the bath by either of the aforementioned expedients or by any other means, operation of the cell pursuant to the aforementioned Patent No. 2,848,397 can be controlled by reference to the open-circuit back electromotive force (hereinafter referred to as B.E.M.F.). A B.E.M.F. of about 2.4 volts is indicative of such difiusion of titanium ions through the porous cathode and into the anolyte as to preclude deposition of metallic titanium predominantly on the distal surface of the cathode. On the other hand, a B.E.M,F. in excess of about 3.1 to 3.2 volts corresponds to an electrode potential of sufficient magnitude (about 1.4 volts) to effect deposition of alkali metals from the bath and thus to seriously reduce the current efficiency. It is readily apparent, therefore, that under any conditions of cell geometry, an increase in cell current, and therefore of cathode current density, will 3,082,159! Patented Mar. 19, 1963 produce an increased IR drop in the cathode deposit with a corresponding increase in the B.E.M.F. On the other hand, the cathode current density is a measure of the productivity of the cell, and an increase in cathode current density will result in an increase in cell output. Consequently it is axiomatic that the cell operation is preferably controlled so as to achieve the maximum cathode current density consistent with a B.E.M.F. which does not exceed about 3.1 to 3.2 volts.

I have now discovered that the current density at the distal surface of the cathode in the aforementioned cell operation can be materially increased Without increasing the B.E.M.F. of the cell by a combination of operating procedures which do not impair the operation of the cell or the quality of its product titanium. That is, I have found (a) that if free metallic titanium, other than the cathode deposit, is present in the catholyte, (b) that if the introduction of titanium tetrachloride into the catholyte is interrupted when the titanium concentration in the catholyte has substantially reached the maximum value consistent with the maintence of the porosity of the metallic titanium deposit on the distal surface of the cathode, and (c) that if during this interruption in titanium tetrachloride feed a supplemental deposition current is supplied to the distal surface of the cathode for a period of time while otherwise continuing operation of the cell, the cathode current density can be increased, with a corresponding increase in cell output, without increasing the B.E.M.F. above the acceptable operating level.

Accordingly, the improvement of my invention relates to the electrowinning of metallic titanium by electrolysis of a fused halide salt bath containing titanium trichloride and titanium dichloride in solution. In this electrolysis, metallic titanium is deposited on the cathode and chlorine is evolved at the anode, the effective anode and cathode surfaces being in direct communication with one another through an anolyte portion of the bath uninterrupted by any physical barrier other than a pervious cathode deposit of metallic titanium on the cathode. The metallic titanium is deposited from the catholyte portion of the bath in contact with that surface of an initially perforate cathode which is distal with respect to the anode as a result of the flow of electrolyzing current through the perforate cathode and through a porous metallic titanium deposit thereon in its passage between the anode and the effective distal surface of the cathode. Titanium tetrachloride is introduced into the catholyte portion of the bath in order to supply the titanium in solution therein in the substantially maximum concentration which permits the maintenance of the porosity of the metallic titanium deposit on the distal surface of the cathode.

These and other novel features of the invention will be more fully understood from the following description taken in conjunction with the drawings in which:

FIG. 1 is a section in elevation of an electrolytic cell arrangement useful for practicing the invention, and

FIG. 2 is a schematic wiring diagram for the cell under these operating conditions.

The improvement in the foregoing operation pursuant to my invention includes, as one condition, the provision in the catholyte portion of the bath of free metallic titanium other than that of the cathode deposit. My new operative procedure further includes the interruption of the introduction of titanium tetrachloride into the bath for a period of time after the aforesaid concentration of titanium in solution has been obtained. Thereafter, for at least a portion of this period of interruption, a supplemental deposition current is imposed upon the electrolyzing current from an electrode which is positioned in the catholyte and which is anodic with respect to the distal surface of the cathode. The interruption of the titanium tetrachloride feed is continued for a sufficient period of time to permit the electrolyzing current to reduce the concentration of titanium in solution in the catholyte to below about 1% by weight, and then the introduction of titanium tetrachloride into the bath is resumed. In the presently preferred practice of my invention, this cycle is repeated until the cathode deposit has to be harvested.

The molten salt baths which are useful in practicing the invention comprise one or more of the halides of the alkali metals and alkaline earth metals. Thus, the chlorides, bromides, iodides and fluorides of sodium, potasslum and lithium as well as the same halides of calcium,

magnesium, barium and strontium may be used with advantage. However, in the interest of simplifying the recovery of the halogen which is liberated at the anode during electrolysis, I presently prefer to use only the chlorides of these metals. Although an individual halide may be used as a single constituent bath, I now prefer to use a combination of these halides inasmuch as such combinations are characterized by relatively lower melting points than the individual salts. It is particularly advantageous, when using a combination of the aforementioned halides, to mix these halides in proportions approximating a eutectic composition in order to obtain baths with low melting points. For example, I have used with particularly satilsfactory results a eutectic mixture composed of mol percent of sodium chloride, 40 mol percent of potassium chloride and 55 mol percent of lithium chloride, the resulting mixture having a melting point of about 350 C. Other useful eutectic mixtures are represented by the mixture composed of 48.5 mol percent of sodium chloride and 51.5 mol percent of calcium chloride having a melting point of 505 C. and by the mixture composed of 24 mol percent of barium chloride, 35 mol percent of sodium chloride and 41 mol percent of potassium chloride having a melting point of 552 C. Of course, as in all other molten salt electrolytic methods for the production of metallic titanium, the bath should be as completely anhydrous as possible and should be compounded of salts of high purity.

The titanium tetrachloride is advar ageously supplied to the bath by introducing it directly into the molten bath either with or without a carrier gas such as argon. The cell atmosphere should, of course, be compartmented to maintain separation between the atmosphere above the portion of the both into which the titanium tetrachloride is introduced and the portion of the bath from which the chloride is evolved at the anode. Moreover, the cell is advantageously tightly closed in order to control the cell atmosphere.

The cell electrodes should be constructed of material which will not introduce extraneous elements into the fused bath. Thus, a non-metallic anode such as graphite or carbon should be used, graphite having been found in practice to be wholly suitable for this purpose. Cathodes of nickel, and preferably of corrosion-resistant nickel base alloys, are useful in practicing the invention. At the prevailing cell temperature, the aforementioned cathode materials have been found not to contaminate the deposited metallic titanium to any significant degree.

The relative position between, and the arrangement of, the anode and cathode within the molten salt body should be such that (a) chlorine evolved at the anode will rise in the anolyte without entering, the catholyte, (b) the anolyte and the catholyte are in communication with one another through a multipli ity of passages, and (c) the distance between the anode and the proximal cathode surface, and hence the resistance of the bath between these surraces, is sufficiently small to permit electrolytically induced depletion of the titanium content of the molten bath between these surfaces.

A number of arrangements of anode and cathode will assure these conditions, and a variety of such arrangements is shown in the drawings in the aforementioned A Patent No. 2,848,397. However, a presently preferred ccll arrangement for practicing the invention is shown in FIG. 1.

As s town in the drawing, a closed cell 1 is provided with a fused salt bath 2 in which a cylindrical cathode is at least partially immersed. The deposition cathode comprises a cylindrical side wall body portion 3 closed at its lower end with an impervious bottom wall portion 4 and an impervious top wall portion 5 extending to and supported on an insulating element 6 by the roof of the cell. The side wall portion 3 is composed advantageously of sheet material having large openings 7 punched at intervals throughout its surface and having a lining of screen material 8 secured to the inner surface of the side wall portion. The impervous bottom wall and side wall portions are constructed of sheet metal composed of a corrosion-resistant nickel-base alloy, and the pervious screen '8 is constructed advantageously of 8-mesh wire screen of the same alloy. The cathode assembly thus encloses an inner body portion A of the fused salt bath 2 which constitutes the aforementioned anolyte.

The anode assembly for the cell comprises a chlorine dome 9 extending downwardly into the interior of the side walls 3 of the cathode assembly, the lower eXtremities of the dome being immersed in the fused salt bath 2. The chlorine dome 9 is advantageously constructed of a corrosion-resistant metal such as nickel in the form of a main frame Ill with an inner lining 11 of alumina brick held in place with refractory cement. The dome is secured to the cover of the cell, and the cover also supports a graphite anode 13 extending into the cell through insulating portions 12 and downwardly into the interior of the cylindrical cathode assembly. The roof of the cell is provided with a port 14 to permit escape of chlorine gas from the surface of the bath within the dome 9, and the cell roof is also provided with a titanium tetrachloride inlet line 15 so as to supply the tetrachloride, either with or without an inert carrier gas such as argon, to the lower portion of the main body portion B of the fused salt bath 2. Any unabsorbed tetrachloride and any inert carrier gas are discharged through another roof port 16. The atmosphere between the upper side wall 5 of the cathode and the chlorine dome 9 may be swept with an inert gas such as argon through an inlet port 17 and an outlet port 18, both in the cell roof.

f a separate auxiliary cathode structure is used in practicing the invention, it is positioned in the main body portion B (the catholyte portion) of the fused salt bath. This structure comprises advantageously a cylindrical body portion 1? supported by a current carrying rod 20 extending into the cell through the cell roof. The body portion of the auxiliary cathode is preferably formed with a relatively large surface area and this has been accomplished in practice by constructing the body portion 19 of wire screen made of 0.08 inch nickel wire and having 4 meshes per lineal inch. However, other types of foraminous conducting material can be used effectively for the auxiliary cathode provided that the openings in the material are not so fine that they will be blocked by small amounts of titanium metal inadvertently deposited on the material during cell operation. A smooth-surfaced, or even a corrugated surfaced, cell wall is also effective as an auxiliary cathode.

In the cell arrangement just described, the chlorine evolved at the anode leaves the surface of the bath within the confines of the silica dome 9 which thus define a compartment C in the cell atmosphere containing the evolved chlorine. The portion of the cell atmosphere exterior of the cathode wall 5 comprises a compartment D into a through which the titanium tetrachloride is introduced. It will be seen, accordingly, that the titanium tetrachloride is absorbed by the body portion B of the bath so that it is added only to that portion of the bath in contact with the auxiliary cathode and with the distal surface of the deposition cathode. The body portion A 3.2 volts.

of the bath, on the other hand, is maintained substantially completely depleted of titanium ions by control of the electrolyzing conditions. The unabsorbed argon is withdrawn from compartment D through an exit line 16 in the cell roof.

The electrolyzing condition which assures the main tenance of titanium-depletion in the body portion A of the molten bath between the anode and the proximal cathode surface, and deposition and maintenance of a porous titanium deposit on the distal surface of the cathode, comprises the use of a voltage sufiiciently high to strip the body portion A of the bath of its titanium chloride content. When the body portion A is effectively stripped of its titanium chloride content thus leaving essentially only the aforementioned eutectic bath composition composed of lithium, sodium and potassium chlorides, the B.E.M.F. of thecell, when measured across the anode and cathode upon opening of the exterior cell circuit, has a magnitude of about 2.6 volts or more when operating with a bath temperature of about 550 C. A B.E.M.F. below about 2.4 'volts is an indication of the presence of titanium chloride in the body portion A. As the upper limit of about 3.3 volts is exceeded, and particularly as the B.E.M.F. reaches about 3.4 volts, decomposition of the non-titaniferous bath components such as the alkali metal chlorides begins to occur, It must be understood that, as appreciated by one skilled in the art of fused salt electrolysis, the maximum B.E.M.F. will be influenced by the titanium concentration in the bath, the electrode compositions, by the bath temperature, and by the fact that B.E.M.F. as measured is the average of the voltage between the anode and both the proximal and the distal surfaces of the deposition cathode, but in general it can he stated that under most conditions the presently preferred upon limit for the B.E.M.F is about The B.E.M.F. is maintained within the aforementioned range either by control of the cell voltage, so as to maintain appropriate depletion of titanium ions in the body portion A of the bath, or by controlling the rate at which the titanium tetrachloride is delivered to the cell for assimilation by the molten bath. Measurement of the at intervals of minutes is generally sufiiciently frequent to permit the maintenance of a substantially uniform value at any desired level in the aforementioned range to within about one-tenth of a volt.

The practice of the present invention takes place in the foregoing environment. Under these conditions it is generally observed that the operation produces some finely divided metallic titanium which does not adhere to the cathode and which will therefore constitute a sludge-like mass in the cell. It has also been observed that the use of an auxiliary cathode as described hereinbefore will result in the deposition of some metallic titanium on this electrode. Whether the titanium is obtained by either of these means, or whether it is deliberately added as fines to establish a rapid buildup of the titanium deposit on the distal cathode surface so as to gain cell operation control, this free metallic titanium is the source which is available for consumption by the supplemental deposition current when the titanium tetrachloride supply to the cell is interrupted.

. The supply of titanium tetrachloride under cell electrolyzing conditions results in the build-up of the concentration of titanium in the solution. The dissolved titanium is in the form of titanium trichloride and titanium dichloride. It is desirable that the concentration of dissolved titanium be sufiiciently high to promote effective deposition of metallic titanium on the distal surface of the cathode in the form of a porous and coarsely crystalline deposit. On the other hand, an excessive concentration of dissolved titanium tends to promote diffusion of this titanium into the anolyte portion of the batch and further promotes deposition of titanium within the pores of the cathode deposit with resulting diminution of the desired porosity of the deposit. It is presently preferred to establish during the build-up period a concentration of dissolved titanium of at least about 1% by weight and generally of at least about 2% by weight. A concentration of about 3% by weight, and even higher, can be used with advantage under proper control of other cell operating conditions including such variables as current density, cell geometry, cell size, effective cathode area, the average valence of the dissolved titanium, and the like.

When the aforementioned concentration of dissolved titanium has been built up in the catholyte portion of the bath, the supply of titanium tetrachloride to the batch is interrupted pursuant to the practice of the present invention. The continued flow, however, of the electrolyzing current between the anode and the effective distal surface of the cathode continues the deposition of a porous deposit of metallic titanium on this surface of the deposition cathode. The electrodeposition cathode density is thereupon increased, pursuant to my invention, by superimposing upon the electrolyzing current a supplemental deposition current flowing from an electrode which is positioned in the catholyte portion of the bath and which is anodic with respect to the distal surface of the cathode. It will be readily appreciated, accordingly, that the supplemental deposition current does not flow through the electrolyte in the titanium deposit on the cathode and thus does not contribute a measurable or significant voltage drop through this deposit and the cathode. Thus, the supplemental deposition current increases the total deposition current to the surface of the titanium deposit, and correspondingly increases the eelctrodeposition current, without increasing any component of the B.E.M.F. until close to the end of this operating phase when the titanium concentration in the catholyte has been significantly lowered.

The supplemental deposition current can be supplied by any electrode positioned in the catholyte portion of the bath which is made anodic with respect to the deposition cathode. A representative, but not limitative, schematic wiring diagram for an electrolytic cell to be operated pursuant to this invention is shown in FIG. 2. The cell 1 contains a deposition cathode 3, an anode 13 and an auxiliary cathode 19. The electrolyzing current is supplied by a source 21 having its negative side connected to both the deposition cathode 3 and the auxiliary cathode 19. The connection to the auxiliary cathode, however, is through a switch 22 which is normally closed during the build-up of the concentration of dissolved titanium, and the distribution of current between the anode and the deposition and auxiliary cathode is controlled by a variable resistance 23. The positive side of the current supply source 21 is connected directly to the anode and is further connected through a second variable resistance 24 and a second switch 25 to the auxiliary cathode 19. After the desired concentration of dissolved titanium has been built up in the catholyte portion of the bath, the switch 22 is open andthe second switch 25 can thereafter be closed in order to make the auxiliary cathode 19 anodic with respect to the deposition cathode 3. It must be understood, however, that these same connec tions can be made to the walls 1 of the cell in lieu of the auxiliary cathode 19, or that both the cell walls and the auxiliary cathode can be used conjointlyf In either event, the amount of supplemental deposition current is controlled by the second variable resistance 24 in such manner as to maintain proper control over the average valence of the dissolved titanium in the catholyte.

The supplemental deposition current at the now-anodic surface in contact with the catholyte solubilizes any metallic titanium thereon and oxidizes divalent titanium ions to trivalent ions in the catholyte. The resulting trivalent titanium ions react with the aforementioned free titanium to form more divalent titanium (in the form of titanium dichloride). Accordingly, the magnitude of the supplemental deposition current should not be so exces- :sive under tne prevailing cell geometry and related conditions as to produce trivalent titanium substantially faster than this trivalent titanium can be reduced by the free metallic titanium to divalent titanium. In general, I have found that the supplemental deposition current can be as high as about 30-35% of the total electrodeposition current at any instant without causing the average valence of the dissolved titanium to rise so high as to adversely affect the quality of the electrodeposited titanium.

After the flow of titanium tetrachloride to the catholyte has been interrupted and the flow of supplemental deposition current has been established, these conditions are maintained while the electrolyzing current depletes the dissolved titanium content of the catholyte to a value below about 1% by Weight, and generally to about A g; (.9 each run. In reporting the conditions prevailing in these runs in tabular form, the following terms are used:

Electrolyzing Current Crystallinity is the percentage of +200 mesh titanium metal in the total metal recovered from the deposition cathode deposit.

Run

to /2% by weight. By thus employing the supplemental deposition current when the dissolved titanium content of the catholyte is within the aforementioned maximum and minimum values, the electrodeposition cathode current density can be increased under catholyte composition conditions which are conducive to the maintenance of a coarsely crystalline porous cathode deposit. When the dissolved titanium concentration has been lowered to be low about 1% by weight, but not below about A% by weight, the flow of titanium tetrachloride to the catholyte is resumed. The supplemental electrodeposition current is also terminated and the build-up of dissolved titanium in the catholyte is continued until the cycle can be repeated. The number of such cycles is limited only by the attainment of a cathode deposit of such dimensions as to necessitate its harvesting. It must be understood, however, that operating conditions may dictate omission of the use of the supplemental deposition current during one or more of the partial-stripping phases of these cycles. Thus, the operation defined in'the claims is only that portion of the complete operation, and consisting of at least one and up to all cycles thereof, in which the supplemental deposition current is used during the partial-stripping phase of that cycle.

The following example is illustrative of the practice of my invention. The cell arrangement was substantially as shown in FIG. 1 and the Wiring arrangement was substantially as shown in FIG. 2 except that the cathodic and anodic connections to the auxiliary cathode 19 were supplemented by similar connections to the metallic cell Walls which thus supplemented the action of the auxiliary cathode during both the titanium build-up and titanium stripping phases of the cell operation. Each of the runs consisted of three cycles, each cycle consisting of a build-up phase followed by a stripping phase. In all runs, the titanium tetrachloride feed was discontinued during the stripping phases but was continued throughout each build-up phase. In runs A and C, no supple mental electrodeposition current Was used during the stripping phases, but in run B a supplemental electrodeposition current was used in the second and third stripping phases only whereas in run D the supplemental electrodeposition current was used in all three stripping phases. In runs A and B, no metallic titanium fines were added to the cell, but in runs C and D titanium fines were added to the catholyte during the first build-up phase of I claim:

1. In the electrowinning of metallic titanium by electrolysis of a fused halide salt bath containing titanium trichloride and titanium dichloride in solution wherein metallic titanium is deposited on a cathode and chlorine is evolved at an anode, the eifective anode and cathode surfaces being in direct communication with one another through an anolyte portion of the bath uninterrupted by any physical barrier other than a pervious cathode deposit of metallic titanium on the cathode, the metallic titanium being deposited predominantly from a catholyte portion of the bath in contact with that surface of an initially perforate cathode which is distal with respect to the anode as a result of the flow of electrolyzing current through the perforate cathode and through a porous metallic titanium deposit thereon in its passage between the anode and the effective distal surface of the cathode, titanium tetrachloride being introduced into the catholyte portion of the bath in order to supply the titanium in solution therein in a substantially maximum concentration which permits the maintenance of the porosity of the metallic titanium deposit on the distal surface of the cathode, the electrolysis taking place in the presence of free metallic titanium other than the cathode deposit, the improvement which comprises interrupting the introduction of titanium tetrachloride into the bath for a period of time after the aforesaid concentration of titanium in solution has been obtained, superimposing upon the electrolyzing current passing through the cathode during at least a portion of said period of interruption a supplemental deposition current flowing directly to the titanium deposit on the deposition cathode from a supplemental electrode which is positioned in contact with the catholyte portion of the bath and which is made anodic with respect to the distal surface of the cathode, the supplemental deposition current comprising up to about 35% of the total deposition current, the interruption of the titanium tetrachloride feed being continued for a suflicient period of time to permit the electrolyzing current to reduce the concentration of titanium in solution in the catholyte portion of the bath to below about 1% by weight, and then resuming the introduction of titanium tetrachloride into the bath.

2. In the electrowinning of metallic titanium by electrolysis of a fused halide salt bath containing titanium trichloride and titanium dichloride in solution wherein metallic titanium is deposited on a cathode and chlorine as L is evolved at an anode, the effective anode and cathode surfaces being in direct communication with one another through an anolyte portion of the bath uninterrupted by any physical barrier other than a pervious cathode deposit of metallic titanium on the cathode, the metallic titanium being deposited predominantly from a catholyte portion of the bath in contact with that surface of an initially perforate cathode which is distal with respect to the anode as a result of the flow of electrolyzing current through the perforate cathode and through a porous metallic titanium deposit thereon in its passage between the anode and the effective distal surface of the cathode, titanium tetrachloride being introduced into the catholyte portion of the bath in order to supply the titanium in solution therein in a substantially maximum concentration which permits the maintenance of the porosity of the metallic titanium deposit on the distal surface of the cathode, the electrolysis taking place in the presence of free metallic titanium other than the cathode deposit, the improvement which comprises interrupting the introduction of titanium tetrachloride into the bath for a period of time after the concentration of titanium in solution has reached at least about 2% by weight, superimposing upon the electrolyzing curernt passing through through the cathode during at least a portion of said period of interruption a supplemental deposition current flowing directly to the titanium deposit on the deposition cathode from a supplemental electrode which is positioned in contact with the catholyte portion of the bath and which is made anodic with respect to the distal surface of the cathode, the supplemental deposition current comprising up to about 35% of the total deposition current, the interruption of the titanium tetrachloride feed being continued for a sufficient period of time to permit the electrolyzing current to reduce the concentration of titanium in solution in the catholyte portion of the bath to below about 1% by weight, and then resuming the introduction of titanium tetrachloride into the bath.

3. In the electrowinning of metallic titanium by electrolysis of a fused halide salt bath containing titanium trichloride and titanium dichloride in solution wherein metallic titanium is deposited on a cathode and chlorine is evolved at an anode, the effective anode and cathode surfaces being in direct communication with one another through an anolyte portion of the bath uninterrupted by any physical barrier other than a pervious cathode deposit of metallic titanium on the cathode, the metallic titanium being deposited predominantly from a catholyte portion of the bath in contact with that surface of an initially perforate cathode which is distal with respect to the anode as a result of the flow of electrolyzing current through the perforate cathode and through a porous metallic titanium deposit thereon in its passage between the anode and the effective distal surface of the cathode, titanium tetrachloride being introduced into the catholyte portion of the bath in order to supply the titanium in solution therein in a substantially maximum concentration which permits the maintenance of the porosity of the metallic titanium deposit on the distal surface of the cathode, free metallic titanium being provided in the catholyte in the form of the fine particles from a previous cathode deposit, the improvement which comprises interrupting the introduction of titanium tetrachloride into the bath for a period of time after the aforesaid concentration of titanium in solution has been obtained, superimposing upon the electrolyzing current passing through the cathode during at least a portion of said period of interruption a supplemental deposition current flowing directly to the titanium deposit on the deposition cathode from a supplemental electrode which is positioned in contact with the catholyte portion of the bath and which is made anodic with respect to the distal surface of the cathode, the supplemental deposition current comprising up to about 35% of the total deposition current, the interruption of the titanium tetrachloride feed being continued for a suflicient period of time to permit the electrolyzing current to reduce the concentration of titanium in solution in the catholyte portion of the bath to below about 1% by weight, and then resuming the introduction of titanium tetrachloride into the bath.

4. In the electrowinning of metallic titanium by electrolysis of a fused halide salt bath containing titanium trichloride and titanium dichloride in solution wherein metallic titanium is deposited on a cathode and chlorine is evolved at an anode, the effective anode and cathode surfaces being in direct communication with one another through an anolyte portion of the bath uninterrupted by any physical barrier other than a pervious cathode deposit of metallic titanium on the cathode, the metallic titanium being deposited predominantly from a catholyte portion of the bath in contact with that surface of an initially perforate cathode which is distal with respect to the anode as a result of the flow of electrolyzing current through the perforate cathode and through a porous metallic titanium deposit thereon in its passage between the anode and the effective distal surface of the cathode, titanium tetrachloride being introduced into the catholyte portion of the bath in order to supply the titanium in solution therein in a substantially maximum concentration which permits the maintenance of the porosity of the metallic titanium deposit on the distal surface of the cathode, and the assimilation of the titanium'tetrachloride into the bath being aided by an auxiliary current flowing between the anode and an auxiliary electrode which is positioned in the catholyte and which is cathodic with respect to the anode and on which some free titanium is formed, the improvement which comprises interrupting the introduction of titanium tetrachloride into the bath for a period of time after the aforesaid concentration of titanium in solution has been obtained, superimposing upon the electrolyzing current passing through the cathode during at least a portion of said period of interruption a supplemental deposition current flowing directly to the titanium deposit on the deposition cathode from the auxiliary electrode which has been made anodic with respect to the distal surface of the cathode, the supplemental deposition current comprising up to about 35% of the total deposition current, the interruption of the titanium tetrachloride feed being continued for a sufficient period of time to permit the electrolyzing current to reduce the concentration of titanium in solution in the catholyte portion of the bath to below about 1% by weight, and then resuming the introduction of titanium tetrachloride into the bath.

5. In the electrowinning of metallic titanium by electrolysis of a fused halide salt bath containing titanium trichloride and titanium dichloride in solution wherein metallic titanium is deposited on a cathode and chlorine is evolved at an anode, the effective anode and cathode surfaces being in direct communication with one another through an anolyte portion of the bath uninterrupted by any physical barrier other than a pervious cathode deposit of metallic titanium on the cathode, the metallic titanium being deposited predominantly from a catholyte portion of the bath in contact with that surface of an initially perforate cathode which is distal with respect to the anode as a result of the flow of electrolyzing current through the perforate cathode and through a porous metallc titanium deposit thereon in its passage between the anode and the effective distal surface of the cathode, titanium tetrachloride being introduced into the catholyte portion of the bath in order to supply the titanium in solution therein in a substantially maximum concentration which permits the maintenance of the porosity of the metallic titanium deposit on the distal surface of the cathode by maintenance of a back electromotive force of 2.4 to 3.2 volts between the anode and the deposition cathode, the electrolysis taking place in the presence of free metallic titanium other than the cathode deposit, the improvement which comprises interrupting the introduction of titanium tetrachloride into the bath for a period of time after the aforesaid concentration of titanium in solution has been obtained, superimposing upon the electrolyzing current passing through the cathode during at least a portion of said period of interruption a supplemental deposition current flowing directly to the titanium deposit on the deposition cathode from a supplemental electrode which is positioned in contact with the catholyte portion of the bath and which is made anodic with respect to the distal surface of the cathode, the supplemental deposition current comprising up to about 35 of the total deposition lcurrent, the interruption of the titanium tetrachloride 3 feed being continued for a sufficient period of time to permit the electrolyzing current to reduce the concentration of titanium in solution in the catholyte portion of the bath to below about 1% by weight, and then resuming the introduction of titanium tetrachloride into the bath.

6. In the electrowinning of metallic titanium by electrolysis of a fused halide salt bath containing titanium trichloride and titanium dichloride in solution wherein metallic titanium is deposited on a cathode and chlorine is evolved at an anode, the effective anode and cathode surfaces being in direct communication with one another through an anolyte portion of the bath uninterrupted by any physical barrier other than a pervious cathode deposit of metallic titanium on the cathode, the metallic titanium being deposited predominantly from a catholyte portion of the bath in contact with that surface of an initially perforate cathode which is distal with respect to the anode as a result of the flow of electrolyzing current through the perforate cathode and through a porous metallic titanium deposit thereon in its passage between the anode and the effective distal surface of the cathode, titanium tetrachloride being introduced into the catholyte portion of the bath in order to supply the titanium in solution therein in a substantially maximum concentration which permits the maintenance of the porosity of the metallic titanium deposit on the distal surface of the cathode, the electrolysis taking place in the presence of free metallic titanium other than the cathode deposit, the improvement which comprises interrupting the introduction of titanium tetrachloride into the bath for a period of time after the aforesaid concentration of titanium in solution has been obtained, superimposing upon the electrolyzing current passing through the cathode during at least a portion of said period of interruption a supplemental deposition current flowing directly to the titanium deposit on the deposition cathode from a supplemental electrode which is positioned in contact with the catholyte portion of the bath and which is made anodic with respect to the distal surface of the cathode, the supplemental deposition current comprising up to about 35% of the total deposition current, the interruption of the titanium tetrachloride feed being continued for a sufiicient period of time to permit the electrolyzing current to reduce the concentration of titanium in solution in the catholyte portion of the bath to below about 1% by weight with a back electromotive force not greater than about 3.2 volts between the anode and the deposition cathode, and then resuming the introduction of titanium tetrachloride into the bath.

7. In the electrowinning of metallic titanium by electrolysis of a fused halide salt bath containing titanium trichloride and titanium dichloride in solution wherein metallic titanium is deposited on a cathode and chlorine is evolved at an anode, the effective anode and cathode surfaces being in direct communication with one another through an anolyte portion of the bath uninterrupted by any physical barrier other than a pervious cathode deposit of metallic titanium on the cathode, the metallic titanium being deposited predominantly from a catholyte portion of the bath in contact with that surface of an initially perforate cathode which is distal with respect to the anode as a result of the flow of electrolyzing current through the perforate cathode and through a porous metallic titanium deposit thereon in its passage between the anode and the etfective distal surface of the cathode, titanium tetrachloride being introduced into the catholyte portion of the bath in order to supply the titanium in solution therein in a substantially maximum concentration which permits the maintenance of the porosity of the metallic titanium deposit on the distal surface of the cathode, the electrolysis taking place in the presence of free metallic titanium other than the cathode deposit, the improvement which comprises interrupting the introduction of titanium tetrachloride into the bath for a period of time after the aforesaid concentration of titanium in solution has been obtained, superimposing upon the electrolyzing current passing through the cathode during at least a portion of said period of interruption a supplemental deposition current flowing directly to the titanium deposit on the deposition cathode from a conductive side wall of the cell in contact with the catholyte portion of the bath and which is made anodic with respect to the distal surface of the cathode, the supplemental deposition current comprising up to about 35 of the total deposition current, the interruption of the titanium tetrachloride feed being continued for a sufiicient period of time to permit the electrolyzing current to reduce the concentration of titanium in solution in the catholyte portion of the bath to below about 1% by weight, and then resuming the introduction of titanium tetrachloride into the bath.

References (Iiteil in the file of this patent UNITED STATES PATENTS 2,741,588 Alpert et a1 Apr. 10, 1956 2,789,943 Kittelberger Apr. 23, 1957 2,848,397 Reimert et al Aug. 19, 1958 2,975,111 Reimert et al Mar. 14, 1961 

1. IN THE ELECTROWINNING OF METALLIC TITANIUM BY ELECTROLYSIS OF A FUSED HALIDE SALT BATH CONTAINING TITANIUM TRICHLORIDE AND TITANIUM DICHLORIDE IN SOLUTION WHEREIN METALLIC TITANIUM IS DEPOSITED ON A CATHODE AND CHLORINE IS EVOLVED AT AN ANODE, THE EFFECTIVE ANODE AND CATHODE SURFACES BEING IN DIRECT COMMUNICATION WITH ONE ANOTHER THROUGH AN ANOLYTE PORTION OF THE BATH UNINTERRUPTED BY ANY PHYSICAL BARRIER OTHER THAN A PREVIOUS CATHODE DEPOSIT OF METALLIC TITANIUM ON THE CATHODE, THE METALLIC TITANIUM BEING DEPOSITED PREDOMINANTLY FROM A CATHOLYTE PORTION OF THE BATH IN CONTACT WITH THAT SURFACE OF AN INITIALLY PERFORATE CATHODE WHICH IS DISTAL WITH RESPECT TO THE ANODE AS A RESULT OF THE FLOW OF ELECTROLYZING CURRENT THROUGH THE PERFORATE CATHODE AND THROUGH A POROUS METALLIC TITANIUM DEPOSIT THEREON IN ITS PASSAGE BETWEEN THE ANODE AND THE EFFECTIVE DISTAL SURFACE OF THE CATHODE, TITANIUM TETRACHLORIDE BEING INTRODUCED INTO THE CATHOLYTE PORTION OF THE BATH IN ORDER TO SUPPLY THE TITANIUM IN SOLUTION THEREIN IN A SUBSTANTIALLY MAXIMUM CONCENTRATION WHICH PERMITS THE MAINTENANCE OF THE POROSITY OF THE METALLIC TITANIUM DEPOSIT ON THE DISTAL SURFACE OF THE CATHODE, THE ELECTROLYSIS TAKING PLACE IN THE PRESENCE OF FREE METALLIC TITANIUM OTHER THAN THE CATHODE DEPOSIT, THE IMPROVEMENT WHICH COMPRISES INTERRUPTING THE INTRODUCTION OF TITANIUM TETRACHLORIDE INTO THE BATH FOR A PERIOD OF TIME AFTER THE AFORESAID CONCENTRATION OF TITANIUM IN SOLUTION HAS 